Carex melanostachya is a rare introduction from Eurasia, first discovered in the flora in Kansas in 1964 (R. L. McGregor et al. 1972). A previous report, as C. nutans Host, from the Montreal area is based on sterile specimens suspected to be of hybrid origin (J. Cayouette and P. M. Catling 1992). A similar taxon, C. songorica subsp. gotoi (Ohwi) Popov [C. gotoi Ohwi] was found once as a waif in Yonkers, New York, in 1895. It differs from C. melanostachya in having perigynia that are shorter, only 3–4 mm, shiny, purplish, and have raised veins.